Non-intrusive error detection techniques for control and shutdown rod position in nuclear reactors

ABSTRACT

Non-intrusive error detection techniques for control and shutdown rod position in nuclear reactors, including methods of monitoring digital rod position indication (DRPI) signals of a DRPI system of a nuclear power plant. The methods include acquiring digital rod position signals at a point between a DRPI display cabinet and a DRPI data cabinet of the DRPI system, and processing the digital rod position signals to identify variations in a signal level and a signal timing of the digital rod position signals to determine rod position errors of the DRPI system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/523,277, filed on Jun. 14, 2012, the contents of which are herebyincorporated by reference herein in their entirety.

FIELD OF INVENTIVE CONCEPT

The present general inventive concept relates to a diagnostic system tomonitor rod position indication signals in a nuclear power plant, andmore particularly relates to systems and methods of performing signaland data diagnostics on control rod position indication systems of anuclear reactor, including non-intrusive error detection techniques forcontrol and shutdown rod position in nuclear reactors.

BACKGROUND

In a Pressurized Water Reactor (PWR), the power level of a nuclearreactor is typically controlled by inserting and retracting controlrods, which for purposes of this application include the shutdown rodsof the reactor core. The control rods are moved by a Control Rod DriveMechanism (CRDM), which typically include electromechanical jacks thatraise or lower the control rods in increments. Known CRDMs include alift coil, a moveable gripper coil, and a stationary gripper coil thatare controlled by a Rod Control System (RCS) and a ferromagnetic driverod that is coupled to the control rod and moves within the pressurehousing. The drive rod includes a number of circumferential grooves atintervals (“steps”) that define the range of movement for the controlrod. For example, a typical drive rod contains approximately ⅝ inchintervals and 231 grooves, although this number may vary.

The moveable gripper coil mechanically engages the grooves of the driverod when energized and disengages from the drive rod when de-energized.Energizing the lift coil raises the moveable gripper coil (and thecontrol rod if the moveable gripper coil is energized) by one step.Energizing the moveable gripper coil and de-energizing the lift coilmoves the control rod down one step. Similarly, when energized, thestationary gripper coil engages the drive rod to maintain the positionof the control rod and, when de-energized, disengages from the drive rodto allow the control rod to move. The RCS typically includes a logiccabinet and a power cabinet. The logic cabinet receives manual demandsignals from an operator or automatic demand signals from ReactorControl and provides the command signals needed to operate the shutdownand control rods according to a predetermined schedule. The powercabinet provides the programmed DC current to the operating coils of theCRDM.

Known PWR designs are challenged in that they do not have adequatedirect indication of the actual position of each control rod. Instead,step counters associated with the control rods are typically maintainedby the RCS and rod position indication (RPI) systems to monitor thepositions of the control rods within the reactor. The associated stepcounter is incremented or decremented when movement of a control rod isdemanded and successful movement is verified. Because the step counteronly reports the expected position of the control rod, certainconditions can result in the step counter failing and deviating from theactual position of the control rod. In certain situations where theactual position of the control rod is known, the step counter can bemanually adjusted to reflect the actual position. However, if the actualposition of the control rod is not known, a plant shutdown may berequired so that the step counters to be initialized to zero while thecontrol rods are at core bottom.

The RPI systems derive the axial positions of the control rods by directmeasurement of drive rod positions. Currently both analog rod positionindication (ARPI) systems and digital rod position indication (DRPI)systems are in use in PWRs. A conventional DRPI system includes two coilstacks for each control rod and the associated DRPI electronics forprocessing the signals from the coil stacks. Each coil stack is anindependent channel of coils placed over the pressure housing. Eachchannel typically includes 21 coils, and the coils are interleaved andpositioned at approximately 3.75 inch intervals (6 steps). The DRPIelectronics for each coil stack of each control rod are located in apair of redundant data cabinets (Data Cabinets A and B). Althoughintended to provide independent verification of the control rodposition, conventional RPI systems are not accurate to fewer than 6steps. For example, the overall accuracy of a DRPI system is consideredto be about ±3.75 inches (6 steps) with both channels functioning and±7.5 inches using a single channel (12 steps).

In contrast to conventional DRPI systems, conventional ARPI systemsdetermine the rod position based on the amplitude of the DC outputvoltage of an electrical coil stack linear variable differentialtransformer. The overall accuracy of a properly calibrated ARPI systemis considered to be about ±7.5 inches (12 steps). Neither conventionalARPI systems nor conventional DRPI systems are capable of determiningthe actual positions of the control rods. In the event of a step counterfailure, plant shutdown for re-initialization of the step counter isrequired as the approximate positions of the control rods reported byconventional RPI are of little or no value.

For purposes of this application, the phrase “control rod” is usedgenerically to refer to a unit for which separate axial positioninformation is maintained, such as a group of control rods physicallyconnected in a cluster assembly. The number of control rods can varyaccording to the plant design. For example, a typical four-loop PWR has53 control rods. Each control rod requires its own sets of coils havingone or more channels and the DRPI electronics associated with eachchannel. Thus, in a typical four-loop PWR, the entire DRPI system wouldinclude 53 coil stacks, each having two independent channels, and 106DRPI electronics units. Further, in this application, the phrase “coilstack” is used generically to refer to the detector coils associatedwith each control rod and should be understood to include either or bothchannels of detector coils. Thus, a measurement across a coil stackcontemplates the value across both channels combined and/or the valueacross a single channel.

Over time, aging and obsolescence issues have led to an increase inproblems with conventional DRPI systems including analog card failuresand coil cable connection problems that, in some cases, may result inunplanned reactor trips. These problems, along with plans for plant lifeextension, have prompted the industry to actively seek viable options tomonitor the health and accuracy of the DRPI systems and/or to replacefailing systems in order to ensure reliable plant operations for decadesto come.

In addition to obsolescence concerns, the lack of diagnosticcapabilities is a significant challenge. Since conventional RPI systemsdo not provide diagnostic information on their health other than thecurrent rod position indication, diagnostics of the RPI system islimited to periods when the PWR is offline. The primary benefit ofoffline diagnostics is to catch obvious failures resulting fromreassembly of the reactor. However, in between refueling outages, RPIfailures can occur without warning, which leads to increased costs forthe plant, especially if replacement parts cannot be obtained in atimely manner. Without active monitoring, plant engineers cannotidentify problems developing in RPI systems and are unable to takepreemptive actions, such as obtaining necessary replacement parts aheadof time and replacing failing components at the next scheduled outage.Instead, plants typically begin remedial actions after an actual failureoccurs.

Beyond the technical challenges of controlling conventional DRPIsystems, regulatory issues exist. Many existing PWRs are approaching theend of qualified life for several components of the conventional DRPIsystems causing a demand for replacement options. There has been asignificant push in recent years for plants to replace aging analogsystems with digital systems made from commercially-availableoff-the-shelf parts. Using readily-available commercial parts provideplants more options for replacement in the future.

BRIEF SUMMARY

Example embodiments of the present general inventive concept provideimproved systems and methods of monitoring digital rod positionindication signals in nuclear power plants. Example embodiments canperform signal and data diagnostics on control rod position indicationsystems in a nuclear power reactor while the reactor is operating.

Additional features and embodiments of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the present general inventive concept.

Example embodiments of the present general inventive concept can beachieved by providing a diagnostic system to monitor digital rodposition indication (DRPI) signals generated by detector coils of a DRPIsystem of a nuclear power plant, including a digital diagnostic unitconnected between a DRPI display cabinet and a DRPI data cabinet of theDRPI system to monitor digital rod position signals of the DRPI datacabinet, wherein the digital diagnostic unit detects variations in thedigital rod position signals to determine rod position errors of theDRPI system.

The digital rod position signals can include rod address signals and rodposition data signals, and wherein the rod position errors aredetermined based on signal level variation and/or signal timingvariation of the rod address signals and the rod position data signals.

The digital diagnostic unit can detect parity bit errors in the digitalrod position signals between the DRPI display cabinet and the DRPI datacabinet.

The digital diagnostic unit can store the measured voltages of thedigital rod position signals when a rod position error or a parity biterror is detected.

The digital diagnostic unit can monitor at least one of the signal levelvariation, the signal timing variation, and the parity bit error of thedigital rod position signals to distinguish between errors of the DRPIdisplay cabinet, the DRPI data cabinet, and/or the detector coils.

The digital diagnostic unit can monitor variations in the digital rodposition signals while the nuclear power plant is operating.

The digital diagnostic unit can monitor variations in the digital rodposition signals to isolate errors of a particular card, cable, orcontrol rod.

The diagnostic unit can monitor the Gray code rod drop signals of thedigital rod position signals.

Example embodiments of the present general inventive concept can also beachieved by providing a method of monitoring digital rod positionindication (DRPI) signals of a DRPI system of a nuclear power plant,including acquiring digital rod position signals at a point between aDRPI display cabinet and a DRPI data cabinet of the DRPI system, andprocessing the digital rod position signals to identify variations in asignal level and a signal timing of the digital rod position signals todetermine rod position errors of the DRPI system.

The method can further include detecting parity bit errors in thedigital rod position data signals between the DRPI display cabinet andthe DRPI data cabinet, and using at least one of the signal levelvariation, the signal timing variation, and the parity bit error todistinguish between errors associated with the DRPI display cabinet andthe DRPI data cabinet.

The method can further include combining the DRPI system with a CoilDiagnostic System (CDS) to distinguish between problems with DRPI coils,the DRPI display cabinet, and the DRPI data cabinet.

BRIEF DESCRIPTION OF THE FIGURES

The above-mentioned and additional features and embodiments of thepresent general inventive concept will become more clearly understoodfrom the following detailed description of the invention read togetherwith the accompanying drawings, in which:

FIG. 1 is a block diagram of conventional DRPI system in a pressurizedwater reactor (PWR), including an example DRPI diagnostic systemaccording to an example embodiment of the present general inventiveconcept;

FIG. 2 illustrates an example embodiment of a Digital Diagnostic Systemto retrofit existing conventional DRPI systems of a nuclear power plant,according to an example embodiment of the present general inventiveconcept; and

FIG. 3 is a diagram of a Digital Diagnostic System (DDS) incommunication with two independent channels of the data cabinets A andB, according to an example embodiment of the present general inventiveconcept.

DETAILED DESCRIPTION

The following description is intended to describe various exampleembodiments of the present general inventive concept, but is in no wayintended to limit its application, or uses. Various example embodimentsare described below in order to explain the general inventive concept byreferring to the figures.

FIG. 1 is a block diagram of a conventional DRPI system in a pressurizedwater reactor (PWR), including an example DRPI diagnostic systemaccording to an example embodiment of the present general inventiveconcept. The DRPI diagnostic system can continuously sense and displaythe positions of each of the control and shutdown rods during plantoperation. This can be accomplished through the use of coil stacks whichare mounted on the rod control housing above the reactor. The coils canbe excited with an AC voltage and magnetically sense the presence of thecontrol rod drive shaft in the center of the coil.

As illustrated in FIG. 1, a typical DRPI system includes a DRPI coilstack 2 including a plurality of DRPI detector coils C₁ to C_(n) tosense the rod position in containment. When the control rod shaft 1enters the coil, it changes the coil impedance to the AC voltageprovided to the coils, thus changing the AC current through the coils.The stepping of rod 1 generates an induced current in the detector coilsC₁ to C_(n) to produce DRPI coil signals. The analog electronics in theexisting DRPI system detect the change in current and create a digitalbit for each coil in the coil stack. Typically, each coil stack 2 is anindependent channel of coils placed over a pressure housing 3 of thenuclear power reactor. These digital bits are transmitted to the controlroom to provide the rod position to a technician via the A and B datacabinets 4 and the display cabinet 5.

DRPI data cabinets A and B (referred to as reference number 4 in FIG. 1)convert the rod position coil signals into digital information. The datacabinets A and B are generally redundant components located insidecontainment to monitor the coil currents and convert them into a digitalposition signal. The digital position information presented to the datacabinets A and B are converted to digital information and transmitted tothe rod position display cabinet 5 in the control room. The displaycabinet 5 addresses the data cabinets A and B, retrieves the digital rodposition information, and displays the rod position on the display. TheDRPI display cabinet 5 can operate under the control of a mastercontroller 20 to display the rod position and diagnostic information,and/or other system information and controls, as desired.

Referring to FIG. 1, the example DRPI diagnostic system 15 can include aCoil Diagnostic System (CDS) 7 and a Digital Diagnostic System (DDS) 22.The CDS 7 and DDS 22 can be formed as independent hardware subsystems,or could be integrated into a single unit. In one example embodiment,the CDS 7 is installed in containment at the DRPI A and B data cabinetsto measure the 21 coil signals from each of the 21 DRPI A or DRPI Bcoils for every rod. The DDS can be connected in the control room at thedisplay cabinet and can observe the digital rod address and digital rodposition data signals between the DRPI A and B cabinets and the DRPIdisplay cabinet.

The CDS 7 and DDS 22 can be integrated with a master controller 20,although it is possible for the components to be formed as separateunits, or as combinations of units, without departing from the scope ofthe present general inventive concept. The master controller 20 caninclude a human-machine interface (HMI) installed in the control room,to interface with the operator or technician. For example, the mastercontroller 20 can include one or more displays and inputs/outputs tointeract and display information to/from the operator or technician, asdesired. The DRPI diagnostic system 15 can provide rod position, coildiagnostics, rod drop timing, digital diagnostics, or other information,to monitor operations of nuclear power plants.

FIG. 2 illustrates an example embodiment of a Digital Diagnostic System(DDS) 22 used to retrofit existing conventional DRPI systems in nuclearpower plants, according to an embodiment of the present generalinventive concept. Referring to FIG. 2, the DDS 22 can be installed inthe control room proximate the display cabinet 5, and can measure thedigital rod address and digital rod position data signals from the DRPIcoil signals, although other locations could be used to house the DDS 22and/or display cabinets. The DDS 22 can be integrated with a mastercontroller 20, including a human-machine interface. The mastercontroller 20 can also be installed in the control room.

As illustrated in FIG. 2, the DDS 22 can acquire rod position signals ata point between the output from the existing DRPI display cabinet 5 andthe DRPI data cabinets 4A, 4B. This enables the DDS 22 to sample theDRPI signal voltages and convert them into digital signals. For example,the DDS 22 can acquire the rod position signals at the test pointsPT₁-PT_(n) (see FIG. 2) in the display cabinets of the conventional DRPIsystem. The test points PT₁-PT_(n) provide access to the rod positiondigital signals, which heretofore were not available during operation.The digital signals are then transmitted to the DDS 22, which may belocated in the main control room. The DDS 22 detects changes in thelevel and/or timing of the digital rod position signals, includingchanges in the rod address and position data information, to determinerod position errors.

Referring to FIG. 2, reference number 24 identifies a typical addressand data communication sequence for a conventional DRPI system. Here,the rod address signals can be sent from the DRPI display cabinet 5 tothe DDS 22. In this embodiment, the rod signals include 7 address signallines (e.g., A0000110, et al.) and 6 data signal lines (e.g., D001111,et al.) for each of the data cabinets 4A, 4B, although various codingschemes and/or protocols could be chosen with sound engineeringjudgment. In this example, the detector/encoder card for the requestedrod's address in the data cabinet can transmit the rod's position in abinary Gray code, wherein the Gray code is comprised of five data bitsand one parity bit. In this case, the parity bit can be a 1 if thenumber of 1's in the address and data bits is odd. This position codecan then be converted to a step number and displayed for that rod. Inthis way, the DDS 22 interprets the Gray code and displays diagnosticand status information.

A system error can be identified as a one bit error which can bedetected from a parity bit check. Other bit errors may include, forexample, a valid rod position code that is mismatched between DRPI A rodposition and DRPI B rod position, which should agree within 12 steps, inthis example.

The DDS 22 can be integrated with a Master Controller and human-machineinterface 20 installed in the control room to form a system providingdigital diagnostics for nuclear power plants. As mentioned above, theDDS 22 can be located in the control room at the display cabinet tomeasure the digital rod address and digital rod position data signals,although other locations could also be used.

FIG. 3 is an example of a DDS 22 in communication with two independentchannels of the data cabinets A and B, according to an exampleembodiment of the present general inventive concept. The illustratedDigital Diagnostic System (DDS 22) is in communication with the datacabinets A and B to sample the DRPI signal voltages and convert theminto digital signals. The DDS 22 interprets the binary digital signalsand displays diagnostic and status information. The components of theDDS 22 are selected to provide sufficient data transmission speeds tosend the sampled data to the master controller and human-machineinterface 20 in real time.

In some embodiments, the DDS 22 can include a plurality of dataacquisition modules to receive the respective DRPI coil signals from theA and B data cabinets. In FIG. 3 the modules are identified asacquisition Module 1 through acquisition module n. Although a variety ofconfigurations for the DDS 22 could be chosen with sound engineeringjudgment, one suitable device for performing the functions of the dataacquisition modules includes an analog-to-digital (A/D) module with a+/−60V input range capable of simultaneous, isolated, high-speed,differential analog acquisition for both the address bus and the databus. The A/D modules can be each connected to an field-programmable gatearray (FPGA) for acquiring various types of signals including thevoltage signals used by the DDS 22. A high speed interface can beprovided to allow an external computer to communicate with the FPGA, forexample at data rates up to 50 MB/s, or higher. As illustrated in FIG.3, the FPGA can be connected to an embedded controller, which can be,for example, a CompactRIO (cRIO) remote high speed interface systemproduced by National Instruments Corporation, which includes swappableI/O modules. The CompactRIO is capable of monitoring the rod address androd position data. In some example embodiments, the DDS 22 is capable ofdriving the rod addresses by using a digital input/output (I/O) modulethat outputs a +/−15V TTL signal to the DRPI data cabinets, but avariety of other types and/or combinations of components could be chosenwith sound engineering judgment to achieve the same or similar results.All such variations are intended to remain within the scope of thepresent general inventive concept. For example, one skilled in the artwill recognize that the general specifications described above for theDDS 22 electronics are not intended to be limiting. A variety of otherconfigurations could be used to acquire sufficient data containinginformation from which the positions of the control rods can be derived.

As described herein, the DDS 22 can distinguish problems with thedisplay cabinet in the control room and problems with the data cabinetsin containment. It can also be used to monitor the Gray code signalsdirectly. When used in conjunction with the CDS 7, the DDS 22 canidentify a problem with a rod's position indication as a coil, datacabinet, or display cabinet problem. Additionally, the DDS is capable ofisolating individual card, cable, and rod problems.

In some embodiments, the DDS 22 can include an embedded system capableof measuring +/−15V signals that are used to transmit the rod addressand rod position data. In these cases, the signals can be monitoredusing an A/D module with a +/−60V input range capable of simultaneous,isolated, high-speed, differential analog acquisition for both theaddress bus and the data bus.

Instructions can be provided to both the FPGA and the real-timecontroller of the embedded system used to compute the positioninformation. For example, in a typical address and data communicationsequence, the rod address can be sent from the DRPI display. Thedetector/encoder card for the requested rod's address in the datacabinet in containment can transmit the rod's position in a binary Graycode. This position is then converted to a step number and displayed forthat rod.

The DDS can also act as a passive or active DRPI digital Gray code roddrop test system. Instructions provided to a real-time controller of theDDS can be used to collect voltage data and log anomalies with theAddress or Data codes. The Master Controller 20 can handle the storageand display of rod diagnostic information.

Instructions provided to the master controller 20, and the DRPIDiagnostic system 15 hardware, enable the system components to be usedas a stand-alone system or for performing temporary diagnostic services.For example, the CDS 7 (FIG. 1) can be used as a stand-alone system,interfacing directly with instrumentation already installed in theplant. Likewise, the DDS 22 is capable of being used as an installedsystem or a temporary diagnostic system. If used as a stand-alonesystem, the CDS and DDS may incorporate a PC running a version of theMaster Controller instructions in order to control the system and viewthe data and diagnostic information.

Conventional DRPI systems can also perform a rod drop time test bymonitoring the voltage across all the coils in the stack while the rodis dropped. The motion of the rod drive shaft through the coil stackinduces a current in the coils which is proportional to the drive shaftvelocity through the coil stack. Rod drop time testing is typicallyperformed after each refueling outage.

Example embodiments of the present general inventive concept provide aDDS module capable of monitoring the digital rod addresses and digitalrod position at the DRPI display cabinet in the control room. Whencombined with the coil diagnostics system at the DRPI data cabinet incontainment, the DDS 22 can identify card problems, cable and connectorproblems, and power supply problems. This will reduce the amount ofreactor trips due to these problems, and minimize the off-line time dueto DRPI reactor trips by identifying the DRPI problem during operationof the reactor.

Example embodiment of the present general inventive concept can beachieved by providing a diagnostic system for a digital rod positionindication (DRPI) system of a nuclear power plant designed to monitor inreal time DRPI signals generated by a plurality of detector coils of theDRPI system while the nuclear power plant is operating, the diagnosticsystem including a digital diagnostic unit connected in parallel betweena DRPI display cabinet and a redundant pair of DRPI A and DRPI B datacabinets, the digital diagnostic unit having inputs configured toreceive DRPI signals communicated between the DRPI display cabinet andthe DRPI A and B data cabinets, a coil diagnostic unit configured toreceive voltage signals from each one of the detector coils, a pluralityof data acquisition modules configured to receive digital rod positionsignals for each detector coil from the DRPI A and B data cabinets, atleast one address input/output module configured to drive rod addressesof the digital rod position signals to the DRPI A and B data cabinets,and a gate array module configured to acquire the digital DRPI signalsfrom the data acquisition and address input/output modules, the gatearray module having an interface connected with a controller to monitorthe digital rod position signals from the DRPI A and B data cabinets foreach coil and identify mismatches between a DRPI A rod position of theDRPI A data cabinet and a DRPI B rod position of the DRPI B data cabinetfor each coil while the nuclear power plant is operating.

Example embodiments of the present general inventive concept can also beachieved by providing a method of controlling and monitoring digital rodposition indication (DRPI) signals of control rods of a DRPI system of anuclear power plant, including generating addresses signals for a subsetof control rods, sequencing through the control rods at a faster ratethan the display cabinet, acquiring digital rod position signals at apoint between a DRPI display cabinet and a DRPI data cabinet of the DRPIsystem, and monitoring the Gray code rod drop signals of the digital rodposition signals at a faster rate to obtain a more accurate timeresolution, thus enabling improved rod diagnostics to detect any slowdown or binding as the rods are dropped.

Example embodiments of the present general inventive concept can also beachieved by providing a method of detecting errors in control andshutdown rod position during operation of nuclear reactors, includingconnecting inputs of a digital diagnostic unit in parallel between adigital rod position indication (DRPI) display cabinet and a redundantpair of DRPI A and DRPI B data cabinets of a DRPI system of a nuclearreactor, receiving DRPI signals that are generated by a plurality ofdetector coils of the DRPI system and communicated between the DRPIdisplay cabinet and the DRPI A and B data cabinets while the nuclearreactor is operating via the inputs, receiving voltage signals from eachone of the detector coils, receiving digital rod position signals foreach detector coil from the DRPI A and B data cabinets, monitoring thedigital rod position signals from the DRPI and B data cabinets for eachcoil, and identifying mismatches between a DRPI A rod position of theDRPI A data cabinet and a DRPI B rod position of the DRPI B data cabinetfor each coil while the nuclear reactor is operating.

Example embodiments of the present general inventive concept can also beachieved by providing a method of detecting errors in control andshutdown rod position during operation of the nuclear power plant usinga diagnostic system for a digital rod position indication (DRPI) systemof a nuclear power plant designed to monitor in real time DRPI signalsgenerated by a plurality of detector coils of the DRPI system while thenuclear power plant is operating, the diagnostic system including adigital diagnostic unit having inputs configured to receive DRPI signalscommunicated between the DRPI display cabinet and the DRPI A and B datacabinets, a coil diagnostic unit configured to receive voltage signalsfrom each one of the detector coils, a plurality of data acquisitionmodules configured to receive digital rod position signals for eachdetector coil from the DRPI A and B data cabinets, at least one addressinput/output module configured to drive rod addresses of the digital rodposition signals to the DRPI A and B data cabinets, and a gate arraymodule configured to acquire the digital DRPI signals from the dataacquisition and address input/output modules, the gate array modulehaving an interface connected with a controller to monitor the digitalrod position signals from the DRPI A and B data cabinets for each coil.

The method can include connecting the inputs of the digital diagnosticunit in parallel between a DRPI display cabinet and a redundant pair ofDRPI A and DRPI B data cabinets of the DRPI system to receive the DRPIsignals that are communicated between the DRPI display cabinet and theDRPI A and B data cabinets, receiving voltage signals from each one ofthe detector coils using the coil diagnostic unit, receiving digital rodposition signals for each detector coil from the DRPI A and B datacabinets using the plurality of data acquisition modules, driving therod addresses to the DRPI A and B data cabinets using the at least oneaddress input/output module, acquiring the DRPI signals from the dataacquisition and address input/output modules using the gate arraymodule, monitoring the digital rod position signals from the DRPI A andB data cabinets for each coil, and identifying mismatches between a DRPIA rod position of the DRPI A data cabinet and a DRPI B rod position ofthe DRPI B data cabinet for each coil while the nuclear power plant isoperating.

It is noted that the simplified diagrams and drawings do not illustrateall the various connections and assemblies of the various components,however, those skilled in the art will understand how to implement suchconnections and assemblies, based on the illustrated components,figures, and descriptions provided herein, using sound engineeringjudgment.

The present general inventive concept can also be embodied ascomputer-readable codes on a computer-readable medium. Thecomputer-readable medium can include a computer-readable recordingmedium and a computer-readable transmission medium. Thecomputer-readable recording medium is any data storage device that canstore data as a program which can be thereafter read by a computersystem. Examples of the computer-readable recording medium includeread-only memory (ROM), random-access memory (RAM), CD-ROMs, DVDs,magnetic tapes, floppy disks, and optical data storage devices. Thecomputer-readable recording medium can also be distributed over networkcoupled computer systems so that the computer-readable code is storedand executed in a distributed fashion. The computer-readabletransmission medium can transmit carrier waves or signals (e.g., wiredor wireless data transmission through the Internet). Also, functionalprograms, codes, and code segments to accomplish the present generalinventive concept can be easily construed by programmers skilled in theart to which the present general inventive concept pertains.

It is noted that numerous variations, modifications, and additionalembodiments are possible, and accordingly, all such variations,modifications, and embodiments are to be regarded as being within thespirit and scope of the present general inventive concept. For example,regardless of the content of any portion of this application, unlessclearly specified to the contrary, there is no requirement for theinclusion in any claim herein or of any application claiming priorityhereto of any particular described or illustrated activity or element,any particular sequence of such activities, or any particularinterrelationship of such elements. Moreover, any activity can berepeated, any activity can be performed by multiple entities, and/or anyelement can be duplicated.

While the present general inventive concept has been illustrated bydescription of several example embodiments, it is not the intention ofthe applicant to restrict or in any way limit the scope of the inventiveconcept to such descriptions and illustrations. Instead, thedescriptions, drawings, and claims herein are to be regarded asillustrative in nature, and not as restrictive, and additionalembodiments will readily appear to those skilled in the art upon readingthe above description and drawings as falling within the scope andspirit of the present general inventive concept, as defined in theappended claims.

The invention claimed is:
 1. A method of detecting errors in control andshutdown rod position during operation of a nuclear power plant using adiagnostic system for a digital rod position indication (DRPI) systemthat monitors in real time DRPI signals generated by a plurality ofdetector coils of the DRPI system while the nuclear power plant isoperating, the diagnostic system comprising a digital diagnostic unithaving inputs configured to receive DRPI signals communicated between aDRPI display cabinet and a redundant pair of DRPI A and B data cabinets,a coil diagnostic unit configured to receive voltage signals from eachone of the detector coils, a plurality of data acquisition modulesconfigured to receive digital rod position signals for each detectorcoil from the DRPI A and B data cabinets, at least one addressinput/output module configured to drive rod addresses of the digital rodposition signals to the DRPI A and B data cabinets, and a gate arraymodule configured to acquire the digital DRPI signals from the dataacquisition and address input/output modules, the gate array modulehaving an interface connected with a controller to monitor the digitalrod position signals from the DRPI A and B data cabinets for each coil,the method comprising: connecting the inputs of the digital diagnosticunit in parallel between the DRPI display cabinet and the DRPI A andDRPI B data cabinets of the DRPI system; communicating the DRPI signalsbetween the DRPI display cabinet and the DRPI A and B data cabinets;receiving voltage signals from each one of the detector coils in thecoil diagnostic unit; receiving digital rod position signals for eachdetector coil from the DRPI A and B data cabinets in the plurality ofdata acquisition modules; driving the rod addresses from the at leastone address input/output module to the DRPI A and B data cabinets;acquiring the digital rod position signals and the rod addresses fromthe data acquisition and address input/output modules in the gate arraymodule; monitoring in the controller the digital rod position signalsfrom the DRPI A and B data cabinets for each coil; and identifyingmismatches between the DRPI A rod position signal of the DRPI A datacabinet and the DRPI B rod position signal of the DRPI B data cabinetfor each coil while the nuclear power plant is operating.
 2. The methodof claim 1, wherein the monitoring further comprises: processing theDRPI A rod position signal and the DRPI B rod position signal andidentifying variations in a signal level and a signal timing of thedigital rod position signals that indicate rod position errors of theDRPI system.
 3. The method of claim 2, wherein the monitoring furthercomprises: detecting parity bit errors in the DRPI A rod position signaland the DRPI B rod position signal and identifying errors associatedwith the DRPI display cabinet and the DRPI A and DRPI B data cabinetsusing at least one of the signal level variation, the signal timingvariation, and the parity bit error.